Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $180.28   13.724%   $205.0216   $205.02   $205.00   $205.00  
  Purchase #2 $177.96   5.656%   $188.0254   $188.03   $188.05   $188.00  
  Purchase #3 $111.52   6.600%   $118.8803   $118.88   $118.90   $118.90  
  Purchase #4 $195.67   6.732%   $208.8425   $208.84   $208.85   $208.80  
  Purchase #5 $234.92   10.480%   $259.5396   $259.54   $259.55   $259.50  
  Purchase #6 $86.26   13.776%   $98.1432   $98.14   $98.15   $98.10  
  Purchase #7 $154.63   6.579%   $164.8031   $164.80   $164.80   $164.80  
  7 purchase totals = $1,141.24       $1,243.2557   $1,243.25   $1,243.30   $1,243.10